1. Field of the Invention
The present invention relates to a scroll type fluid machine.
2. Description of the Related Art
A conventional scroll type fluid machine generally includes a pair of scroll members of the same shape with a certain thickness, which have clockwise- or counter-clockwise-wound scroll teeth engaged 180 degrees out of phase with each other, with one scroll member fixed and the other performing a circling, but not rotating, motion with respect to the fixed member. A fluid is drawn in between the pair of scroll teeth and its volume is progressively reduced and compressed toward the center of a space formed by the paired scroll teeth. As shown in FIG. 9, the scroll tooth is considered as consisting of a plurality of continuous semicircles. If we let R stand for the radius of a smallest semicircle R1 in the upper half of the tooth with respect to the center line, then a smallest semicircle in the lower half has a radius of 2R a second semicircle R3 in the upper half has a radius of 3R, and a second semicircle R4 in the lower half has a radius of 4R, all these semicircles formed continuous. These scroll teeth are so constructed as to engage with each other from their ends toward their centers during the compression stroke.
To allow this motion, bearings that support the scroll members are generally provided outside a scroll disk, and a pin crank mechanism to ensure the circular motion is normally mounted on an outer peripheral portion of the disk.
An example of such a conventional scroll tooth construction is described in Japan Patent Application No. Showa 64-1674.
The conventional scroll type fluid machine has the following problems. As to the shape of the scroll teeth, although the scroll teeth are formed in such a way as to allow the fluid compression up to the central portion of the scroll teeth, when we look at the machine as a compressor, it has a relatively large delivery opening at the center for the delivery pressure of 7 kgf/cm2. So, the compressed space mostly comes to communicate with the delivery opening before the compression reaches the central portion. That is, the mechanism of the central portion is not utilized effectively. Denoted 3a in FIG. 8 is the delivery opening.
Further, because the scroll teeth engage up to the central portion, the bearings supporting the rotation and circling motion are located outside the circling scroll disk in the direction of drive shaft end. This means that the circling scroll disk is supported by the bearing on one side only, degrading the precision of the circling motion. This makes it impossible to elongate the scroll tooth length.
Another drawback is that the bearing cannot be mounted at the position where it can efficiently receive a radial load acting on the scroll tooth that is performing the compression stroke. Because the bearing is installed outside the scroll disk, the bearing is applied a moment, which is a product of the radial load acting on the scroll tooth and the distance to the bearing mounting position. So, the bearing must have an excessively large load withstand strength considering the moment. This bearing position also poses a problem of requiring additional space in the direction of axis.
Further, to achieve a circling motion without rotating the scroll, a pin crank is commonly employed in recent years. The pin crank is usually mounted on the outer periphery of the scroll disk. Because of its mounted position, the pin crank is not free from instability caused by expansion of the circling scroll disk and the accumulated mounting dimension errors of bearing, disk and housing. One of the steps taken to solve these problems is to install a shock absorbing structure in the pin crank bearing. This structure, however, causes the circling scroll to vibrate during the circling motion. These constructions are shown in FIGS. 7 and 8.
As to the capacity increase, which is one of the major market demands, the problem of accuracy is posed by the elongated scroll tooth length. To deal with this problem, there is a conventional method which forms the circling scroll as a twin type. That is, two circling scroll teeth are formed on both sides of the center mirror disk and two fixed scrolls that engage with the circling scroll teeth are provided on the left and right side. This method can make the scroll teeth length short and therefore solve the precision problem. Because the left and right circling scroll teeth are configured symmetrical with respect to the center mirror disk, however, the imbalance in weight results in a dynamic imbalance during the circling motion. To counter this dynamic imbalance, a large balance weight must be installed. The construction of the conventional twin type is shown in FIG. 15.
Further, because this correction of dynamic imbalance requires an additional space and cost, it is not possible to increase the eccentricity, a means to effectively increase the delivery capacity, which means that the capacity increase of the twin-type scroll fluid machine is difficult.